1. Field of Invention
The present invention relates to a light guide plate and surface light source device provided with the light guide plate, and to a display provided with the surface light source device. The present invention is applicable to backlighting of LCD panel used as displaying member for portable phone, game playing machine, electric note book, mobile terminal device or personal computer, or that of display panel for other usages such as advertising.
In addition, the present invention is applied to a light guide plate employed in the surface light source device and a display comprising the surface light source device and displaying member.
2. Related Art
It is known to backlight a displaying member such as LCD panel by an illumination light outputted from a surface light source device. In general, a surface light source device comprises a light guide plate provided with an incidence face and an emission face, and primary light is introduced through the incidence face, an illumination light is outputted toward a displaying member.
Light emitting diode (LED) have been growingly often employed as a primary light source in recent years instead of fluorescent lamp. Document 1 noted below discloses an example of such. LED is small in weight and size (point-like light source), being suitable for making surface light source devices or displays using surface light source devices small in weight and size.
Under such background, a surface light source device (improved art) employing light guide plate 100 as shown in FIG. 18 has been proposed. Referring to FIG. 18, light guide plate 100 first guiding portion 102 and a plurality of second guiding portions 103 bridging first guiding portion 102 to plate-like member (guiding-and-emitting-portion) 101.
Light from LED 107 disposed opposite to end face 106 of first guiding portion 102 travels within first guiding portion 102 in a direction (length-direction; perpendicular to end face 106) along side face 104 of plate-like member 101. It is noted that side face 104 gives a plane (interface) on which a boundary between second guiding portion 103 and plate-like member (guiding-and-emitting-portion) 101 exists.
Second guiding portion 103 causes this light to enter into the inside of plate-like member (light guide plate) 101 from side face 104 thereof, producing an inner propagation light travelling within plate-like member 101. This inner propagation light is emitted gradually from emission face 105 on the way of travelling.
Attention should be paid to a fact such that LED 107 supplies primary light through end face 106 of first guiding portion 102. This means that a primary light source (LED 107) is not required to be disposed opposite to side face 104 of plate-like member 101. Since many second guiding portions 103 optically bridge first guiding portion 102 to plate-like member 101, if LED 107 disposed in the vicinity of end face 106 of first guiding portion 102, light propagating within first guiding portion 102 overall is then transferred to plate-like member 101 via second guiding portion 103 In other words, first guiding portion 102 functions like a kind of “imaginary primary light source”.
As a result, a state like such that a plurality of imaginary primary light sources are disposed along side face 104 depending on number of second guiding portions 103 is realized. This enables emission face 5 to have a uniformalized emission brightness. Such uniformalization, in particular, avoiding the vicinity of side face 104 from showing an uneven brightness is hardly achieved by the prior art disclosed in Document 1, unless primary light sources are actually disposed along side face 104 at a small interval.                Document 1: Japanese Patent Publication Nos.3496806        
Thus the improved art shown in FIG. 18 relaxes a shortage (uneven brightness around side face 104) of the prior art disclosed in the above Document 1.
However, there arises demands for still higher brightness and evenness of illumination light according to growingly improved performance of LCD panel and others.